1. Field of the Invention
This invention relates to a method for determining a specific property of a rotational body, such as surface contour of the roll surface or concentricity, state of oscillation, deflection and the like.
2. Discussion of Background Information
Such a method can be used, for example but not exclusively, for measuring such properties in a web processing machine, such as a paper or board or tissue machine, or else in roll grinding machines.
During the measurement, for example, of the radial concentricity of rotational bodies, such as rolls in a paper machine, in the methods known from the prior art, a signal is picked up with the aid of one or more distance sensors.
In this case, the distance from a fixed point to the roll surface is measured. If the cross section of the roll is exactly round, then no distance change will be measured. If the cross section has irregularities, for example in the form of bulges or corrugations, the distance sensor measures a distance which changes continually.
This measured result indicates the irregularity of the roll surface, if the point of rotation of the rotating roll does not move.
However, if the point of rotation moves, for example because of mechanical oscillations, then a distance sensor measures a distance change even if the cross section is perfect and has no irregularities in the form of bulges and corrugations, for example.
This means that, with a single distance sensor, no distinction can be drawn between mechanical oscillations of the roll and irregularities in the surface contour of the roll surface.
It follows from this that, if only a single distance sensor is used, a signal is measured which is composed of the superimposition of the surface contour of the roll surface and mechanical oscillations of the roll.
The prior art discloses a method in which four distance sensors are arranged over an angle of 180° over the roll circumference. The application of this method in the case of rolls leads to problems which are only accessible to a limited extent. Furthermore, the method is complicated to perform.